U.S. Pat. No. 4,760,421 issued Jul. 26, 1988, and now assigned to the assignee of the present application discloses an electronic printer which utilizes a noncoherent bundle of optical fibers. The fiber ends at one face of the bundle are organized in a linear array. The ends of the same fibers in a second face are organized in an area array which may be, for example, rectangular, square or circular. There is no predetermined relationship between the fiber positions in the linear array face and those in the area array face. Consequently, the bundle is noncoherent.
The fiber bundle is used to transmit light from an array of light sources optically coupled to the area array face of the bundle to, for example, photosensitive, photographic, or electrophotographic medium coupled to the linear array face of the bundle. Each of the fibers in the linear array face represents a pixel in a line of pixels. Illustratively, the light source comprises a cathode ray tube (CRT) operative to generate a localized area of light at each of a sequence of electron beam addresses on the face plate of the tube which is coupled to the area array face and produces the desired sequence of pixels generated at the linear face of the bundle.
The sequence of tube face plate addresses which corresponds to the sequence of pixels in the linear array face of the fiber optic bundle is obtained in accordance with the above-mentioned patent, during an initialization procedure in which light is introduced into individual fibers in the area face of the bundle by a CRT, and a photosensor is moved incrementally along the linear face of the bundle. Illustratively, the photo-sensor is covered by an opaque hood with a narrow transparent slit in it. The slit is narrow compared to a fiber diameter and is moved in increments also small compared to a fiber diameter. Light passing through the slit is incident on the photosensor. This procedure results in the photosensor measuring light unambiguously from only one fiber at a time.
A CRT is used to direct electrons to each of the preestablished beam addresses on the face plate while the photosensor is stationary at a selected position in the linear face. When the photosensor indicates the presence of light in the fiber, the set of electron address for which light appears in the fiber is associated with the photosensor slit position, in each instance, to determine the correspondence between the electron addresses and a pixel position (presumably a fiber end) in the linear face. An optimum address for each pixel is chosen from each set. Because the photosensor is moved from pixel position to consecutive position, a sequence of associated addresses is thus obtained. The resulting table of pixel positions vs. electron beam addresses is stored in a PROM which is interrogated during normal operation of the printer. The interrogation of the sequence of addresses occurs each time a line of pixels is to be generated.
Pixels are excited, at the positions so obtained, during normal operation of the printer, to discharge, for example, consecutive (imaginery) linear segments of a moving electrostatic drum or belt in an electrophotographic process. The discharged medium containing an electrostatic image moves past toner, transfer, and fixer stations in a manner common to commercially available xerographic copiers, to transfer the electrostatic image, so created, to plain paper.
The CRT useful in such a printer is relatively small, essentially about the size of a conventional cigar. The face plate for such a CRT advantageously comprises a disc of small diameter optical fibers. The area face of the fiber optic bundle is abutted against or optically coupled to the fiber optic face plate and permanently fixed in position with respect to the face plate so that light generated at a selected one of the face plate addresses enters the end of a fiber in the area face of the bundle and excites a corresponding pixel in the linear face.
Although CRT's of this type are available commercially, they are made in relatively small quantities at present and thus are relatively expensive. They are presently used primarily for head-up displays in military vehicles. Stability of the electron beam position typically requires elaborate feedback control in such equipment.